How important is 100B Market Cap for Bitcoin? Is it the bottom?
Not important and surely not the bottom. I don't think market cap could be sort of a support for price. I know that round number prices can be a psychological support/resistance but I think it doesn't really apply to market cap. Speaking of the bottom, I'm still expecting Bitcoin to break yearly low of $5700. I've lost count how many times Bitcoin has touched $6000 only to rebound shortly after. I'm really really waiting for cheap coins 
What you really need to look into to know If we're progressing or not is the number of ATMs, services, local shops etc. that accepts bitcoin and how are they growing over the months.
I don't think small merchant acceptance and ATMs are still relevant these days. Pretty sure we've moved on and people might have realized that Bitcoin isn't really the best tools for daily payment for now. What people expect now is adoption by huge financial institutions and easier access for major investment Bitcoin from big firms and common people.